Standing balance in aging is robust against head rotation during visual tracking

Abstract

Standing balance is relatively more unstable when visually pursuing a moving target than when fixating a stationary one. These effects are common across age groups if the head is restrained during visual task performance. The present study focused on the role of the head motion on standing balance during the pursuit of a moving target as a function of age. Three predictions were tested: a) standing balance is compromised to a greater extent in older than young adults by gaze target pursuit compared to fixation, b) older adults pursue a moving target with greater and more variable head rotation than young adults, and c) greater and more variable head rotation during the gaze pursuit task is associated with greater postural sway. Twenty-two (22) older and twenty-three (23) young adults stood on a force plate in front of a 60-inch monitor while performing two visual tasks: fixation at a stationary target and gaze pursuit of a horizontally moving target. Centre of pressure (CoP) and head kinematics were synchronously recorded with the Vicon motion analysis system, while head-unconstrained gaze was captured by the Pupil Labs Invisible mobile tracking system. Postural sway, reflected in the interquartile CoP range and the root mean square (RMS) of CoP velocity increased during the gaze pursuit compared to the fixation task (p<.05), and this effect was more pronounced in older than young participants (p<.05). Older adults pursued the moving target employing more variable (p=.022) head yaw rotation than young participants although the amplitude of head rotation was not systematically different between groups (p=.077). The amplitude and variance of head yaw rotation did not correlate with postural sway measures. Results suggest that older adults may engage more variable head rotation when tracking a moving target to compensate for age-related deficits in eye smooth pursuit movement. However, this strategy does not seem to compromise standing balance.